In an optical communication system, it is typically necessary to couple an optical fiber to a transmitter, receiver or transceiver device. Such a device typically includes one or more optical connectors for this purpose. An optical cable comprising a fiber terminated with a plug can be coupled to the device by inserting the plug into the connector. The transmitter, receiver or transceiver device typically includes an opto-electronic device, such as a light source or light sensor, a receptacle that mates mechanically with the plug in a position in which the fiber end is optically aligned with the opto-electronic device, and a retaining mechanism that inhibits inadvertent unplugging.
Coupling an optical fiber to a transceiver device can be facilitated by modularizing the transceiver device. For example, as illustrated in FIG. 1, a known optical transceiver module 2 has a configuration or form commonly referred to as a Small Transceiver Format or Small Form Factor format. The transceiver module 2 includes a metallic module housing comprising an upper metallic housing portion 13 and a lower metallic housing portion 14 that together form a substantial portion of the module housing. Although the transceiver module 2 includes both a transmitter system and a receiver system in a side-by-side arrangement in the module housing, only the transmitter system is shown in FIG. 1 for purposes of clarity, as the receiver system is similar.
An optical fiber cable that includes a plug 8 and a sheathed fiber 9 having a fiber end retained in a ferrule 12 of plug 8 can be mated with the transceiver module 2 by plugging the plug 8 into a receptacle assembly 5. A latch 15 of the plug 8 latches the plug 8 to the transceiver housing to maintain the plug 8 and the receptacle assembly 5 in locking engagement with each other.
When the plug 8 is mated to the receptacle assembly 5, the ferrule 12 is contained within the receptacle assembly 5. The receptacle assembly 5 is connected to a transmitter subsystem 16 (also commonly referred to as a transmitter package) of the transceiver module 2. Transmitter subsystem 16 has a configuration or form that is typically referred to as a transistor outline (TO)-can. The transmitter subsystem 16 typically contains a laser diode chip, one or more lenses that make up an optics system (not shown), and one or more other electronic components mounted on a transmitter submount assembly (not shown).
When the plug 8 is mated to the receptacle assembly 5, the end of the optical fiber retained in the ferrule 12 is optically aligned with the optics system of the transmitter subsystem 16. Electrical leads 18, 19, 21, 22, etc., pass through the TO header 17 and communicate electrical signals between traces on the transmitter submount assembly and electrical circuitry (not shown) in the transceiver module 2 that is external to the transmitter subsystem 16. An electrical signal ground region 23 on the TO header 17 carries the signal ground for the electrical components of the transmitter subsystem 16. In some types of transceiver modules, a metal enclosure similar to the TO header 17 carries the signal ground. Other electrical components of the transceiver module 2 that are external to the transmitter subsystem 16 are electrically grounded by connecting their ground contacts (not shown) together and to the signal ground region 23 and all together to the upper or lower metallic housing portions 13 and 14, through the metallic receptacle assembly 5. This metallic housing electrical ground connection is referred to as the chassis ground.
In some instances, in order for the transceiver module 2 to operate properly, the signal ground region 23 or other structure that carries the signal ground and the module housing or other structure that carries the chassis ground need to be electrically isolated from each other. However, as the receptacle assembly 5 is normally made of metal and is in direct contact with the housing portions 13 and 14, which are at the chassis ground potential, isolating these grounds from one another can be problematic.
As illustrated in further detail in FIG. 2, the receptacle assembly 5 has a generally cylindrical receptacle 25 that mates with the plug 8 and a generally cylindrical coupling portion 27 that allows the receptacle assembly 5 to be securely attached to the transmitter subsystem 16. Between the receptacle 25 and the coupling portion 27 is a ring-like connector portion 26 defined by a cylindrical portion 26A and flanges 26B and 26C. The connector portion 26 is the part of the receptacle assembly 5 that mechanically mates with mating features of the housing portions 13 and 14. The shape of the connector portion 26 and its attachment to the housing portions 13 and 14 ensures mechanical and optical alignment of the fiber end contained in the ferrule 12 with the optics system of the transmitter subsystem 16. Because the receptacle assembly 5 is made of metal, it provides shielding against electromagnetic interference (EMI), which is desirable. However, because the connector portion 26 of the receptacle 5 is normally in physical contact with the upper and/or lower housing portions 13 and 14, electrically isolating the signal ground from the chassis ground can be problematic.